Head injury is a leading cause of death and acquired disability in childhood. However, the biomechanics of pediatric head injury are poorly understood, primarily due to, the paucity of age-specific data regarding mechanical properties of immature tissue and its response to specific loads. The interdisciplinary proposed research plan is designed to answer the following question: What mechanisms cause what injuries in children of what age? The long-term objectives of the proposed research plan are to determine mechanical properties of the skull and brain, the loads they can withstand safely, and unique mechanisms for primary brain injury in infants (less than 3 months) and young children (1-3 years). In so doing, the long term impact of proposed research plan will be to open pathways for enhanced traumatic head injury prevention, detection, and treatment strategies specific to infants and toddlers. Both contact and non-contact mechanisms of brain injury will be investigated. The research plan uses an integrated bioengineering approach consisting of animal experiments, human and animal tissue tests, clinical studies, and anthropomorphic surrogates, all complemented by mathematical models to: A) measure pediatric tissue injury thresholds for acute neural, vascular, and blood-brain barrier damage B) measure pediatric skull and brain tissue mechanical properties C) create computational models for infant and toddler head injury using (A) and (B) D) qualitatively validate the computational model predictions with witnessed accidental head injuries in children E) measure loads experienced anthropomorphic surrogates during falls, shakes, and inflicted impacts F) determine the relative roles of impact forces and inertial loads in the etiology of primary brain injuries G) compare the computational simulations with acute clinical data to infer potential mechanisms of injury in non-accidental head injury. The overall hypotheses of the proposed research program are that 1) thresholds for skull fracture and tissue injury and mechanical properties of the brain and skull vary with age, such that both contribute to differences in primary head injuries between infants and toddlers, and 2) the increased compliance of the infant skull results in greater brain tissue injury from impact trauma; and 3) a valid computational model can be created to predict specific primary injuries resulting from a given reported mechanism.